US 4,979,815 AGranted

Laser range imaging system based on projective geometry

OwnerConstantine J. Tsikosinventor

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Abstract

A range imaging system, and a method for calibrating such a system are based on the principles of projective geometry. The system comprises four subsystems: (1) a laser and a cylindrical lens or vibrating mirror for producing a planar beam of light; (2) an electronic camera equipped with a lens and an appropriate interference filter; (3) an electronic circuit for height (depth) measurements and video image generation; and (4) a scanning mechanism for moving the object with respect to the light beam and the camera so as to scan an area of the object surface. The system is calibrated by determining the position in the electronic image of the object surface at three different heights. The range image is generated from these three known heights from either a previously determined look-up table, or from a calculation based on the invariance of the cross-ratio, a well known ratio from projective geometry.

Claims87

Dependent claims

Apparatus for producing a range image of an area of the surface of an object, said apparatus comprising, in combination:

(a) light source means for projecting a substantially planar light beam onto said object surface to illuminate said surface along a light stripe;
(b) electronic camera means, arranged to view said object surface, as illustrated by said light beam, at an angle with respect to the plane of said light beam, for converting the viewed image into an electronic representation thereof which is divided into a plurality of picture scan elements;
(c) electronic signal processing means, coupled to said electronic camera means, comprising:
(1) means responsive to said electronic representation of said image, for determining the relative position, within said electronic representation, of the scan elements thereof corresponding to said light stripe on said object surface, said position determining means including means for counting the number of scan elements in said electronic representation of said image from a known line of said image to said scan elements corresponding to the image of said light stripe;
and
(2) table look-up means responsive to said position determining means for determining the height of said object surface at a plurality of points along said light stripe;
(3) means responsive to said height determining means for storing each height in association with its respective point of said object surface;
and
(d) means for moving at least one of (i) said object with respect to said light source means and said camera means and (ii) said light source means and said camera means with respect to said object, thereby to scan an area of said object surface with said planar light beam.

6 more elements

Apparatus for producing a range image of an area of the surface of an object, said apparatus comprising, in combination:

(a) light source means for projecting a substantially planar light beam onto said object surface to illuminate said surface along a light stripe;
(b) electronic camera means, arranged to view said object surface, as illuminated by said light beam, at an angle with respect to the plane of said light beam, for converting the viewed image into an electronic representation thereof which is divided into a plurality of picture scan elements;
(c) electronic signal processing means, coupled to said electronic camera means, comprising:
(1) means, responsive to said electronic representation of said image, for determining the relative position, within said electronic representation, of the scan elements thereof corresponding to said light stripe on said object surface;
(2) means responsive to said position determining means for determining the height of said object surface at a plurality of points along said light stripe, said height determining means including means for determining the height (h) of said object surface at a plurality of points (1, 2, 3 . . . i . . . N) along said light stripe in dependence upon the heights (h(A), h(B), h(D)) of three known points (A,B,D) and the cross ratio (d(A), d(B), d(i), d(D)) with respect to point i, where "d" is the position of the respective point;
(3) means responsive to said height determining means for storing each height in association with its respective point on said object surface;
and
(d) means for moving said object with respect to said light source means and said camera means so as to scan an area of said object surface with said planar light beam.

5 more elements

Dependencies are inferred from the claim text.